Fixed step count stepper

Fixed step count stepper

The Fixed Count Stepper provides a way to step the frequency in a band/decade/octave with a configured number of steps. The following examples explain how to calculate the frequency step size using the Fixed Count Stepper configured for step per decade.

Example 1: Linearly dividing a decade in x number of steps

Suppose we have the frequency range of 1 kHz to 10 kHz, which is one full decade apart from each other. If we linearly divide this decade into 10 steps, we would end up with the following series: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 kHz.

Example 2: Stepping through a frequency range that is part of a full decade

Now, let's consider the frequency range of 5 kHz to 10 kHz, which is not a full decade apart from each other. We can still perform 10 steps/decade by testing the series 5, 6, 7, 8, 9, 10 kHz, which is a linear division of the full decade from 1 kHz to 10 kHz. In this case, because the start frequency is higher than the start of the decade, less steps need to be tested, but it is still done based on the configured 10 steps/decade.

Example 3: Using logarithmic stepping and starting frequency

Suppose we use logarithmic stepping to divide the full decade (1 kHz to 10 kHz) into 10 steps/decade. We might end up with a frequency series that includes a frequency value of 4.9 kHz, which is not part of the specified frequency range of 5 kHz to 10 kHz. In this case, the next frequency in the series might be 5.7 kHz, which becomes the start frequency for the test because it is the first frequency in the series that is above the configured start frequency of 5 kHz. This behavior is similar to Example 2.

Example 4: Stepping through a frequency range that is not a full decade apart from each other

Suppose we have the frequency range of 5 kHz to 20 kHz, which is not a full decade apart from each other. If we see this frequency range as part of a full decade starting from 5 kHz to 50 kHz, where we expect to perform 10 steps/decade, we would linearly end up with the following series: 5, 10, 15, 20 kHz of frequencies to be tested. If we logarithmically divide the 10 steps over the decade from 5 kHz to 50 kHz, 5 kHz is always found in the series because it is used as the base of a decade.

In RadiMation, we determine the decades based on the series 0.1, 1, 10, 100, etc. for best reproducibility. The resulting stepped frequencies will always be the same for each different "decade", regardless of the configured start frequency. Each decade is divided by the selected number of steps, after which the remaining points in the configured frequency range set by the end-user are tested.

Therefore, if you use a Fixed Count Stepper with 10 logarithmic steps per decade and a configured start frequency of 200 Hz, the actual start frequency may be slightly different due to the logarithmic stepping. In this case, the start frequency might be 215 Hz instead of the configured 200 Hz.